As known well, concrete is a composite material which utilizes the fact that, when water is added to gravel, sand and cement and is kneaded together with the latter, the water and the cement are hardened under hydration reaction. Since the concrete is long in durability, and is high in strength and, further, is low in cost, the concrete is widely used in various fields. Particularly, the concrete is a material which is essential for buildings and civil engineering construction. However, the concrete alone is extremely low in bending strength and tensile strength, and cannot sufficiently stand up against a bending force and a tensile force. In order to strengthen or reinforce this disadvantage, a method has been invented which utilizes concrete reinforced with steel products. It is the existing condition that the compound of the concrete and the steel products is widely utilized for many buildings as reinforced concrete or steel concrete.
It cannot be avoided that, as a basic property of the concrete dry shrinkage occurs due to evaporation of excess mixed water during hardening, and many minute cracks are generated at various locations. The cracks per se are elucidated in view of structural mechanics, to be of no problem. However, secondary influences caused by the cracks, for example, leaking of rain in a concrete building, corrosion or erosion of reinforcement due to leaking water from cracks, reduction in structural strength caused by the corrosion, and the like, are so serious as to down grade a material value of the concrete. Accordingly, when cracks occur in the concrete or the reinforced concrete, it is essential to repair the cracks. Conventionally, the following repairing methods are employed.
Repairing methods normally practiced conventionally are divided broadly into two categories, depending upon the size or dimension of the cracks.
The first method is one which is employed in the case where crack width is relatively wide such as those above a value of the order of 1 mm, and a repairing material can easily be poured into the cracks. In the method, a concrete surface is cut out in the form of a letter x or x along the cracks, a repairing agent such as cement milk, mortar or the like is poured into the cracks by the use of a simple appliance and, subsequently, the cut-out portions are filled up by cement mortar or resin mortar, to repair the cracks.
The second method is one in which various injection appliances are used to inject, under pressure, a repairing agent such as resin or the like into cracks. The method is utilized in the case where the crack width is of the order of 1 mm or less, and the repairing material like one described above cannot easily be poured into the cracks. In this case, the narrower the crack width, and the deeper the depths of the cracks, the larger the injection resistance. Accordingly, various appliances are used which are so contrived that elastic springs, hydraulic pressure or pneumatic pressure, or rubber elasticity is utilized to produce a predetermined injection pressure. Various examples of the appliances are shown in FIGS. 12 through 15.
An appliance illustrated in FIG. 12 is one in which an elastic force of a rubber tube is utilized to produce injection pressure. The arrangement is such that a resin (a repairing agent) 2 is forced into a rubber tube 1 by a grease pump to inflate the rubber tube 1 like a balloon, and a contractile force of the rubber tube 1 causes the resin 2 to be injected into the cracks.
An appliance illustrated in FIG. 13 is one which is arranged such that a resin is put in a cylinder 3 in the form of an injector or syringe made of a plastic material, and a contractile force of rubber straps 4 and 4 causes a piston to be pushed into the cylinder to inject the resin.
An appliance illustrated in FIG. 14 is one which is arranged such that a pressure tank 6 having a check valve 5 is mounted on cracks, resin 2 is injected into the pressure tank 6 by a grease pump 7 to increase or raise air pressure within the pressure tank 6, and the air pressure causes the resin 2 to be injected into the cracks.
An appliance illustrated in FIG. 15 is one which is arranged such that an elastic spring 10 is arranged at a rear portion of an internal pressurizing plug 9 of a cylinder 8 in the form of a syringe, a lever 11 connected to the internal pressurizing plug 9 is pulled back end to draw the resin 2 into the cylinder 8 and, simultaneously, the elastic spring 10 is contracted, and an elastic repelling force of the elastic spring 10 causes the pressurizing plug 9 to be pushed forwardly to inject the resin 2 into the cracks.
In addition to the above-described appliances, there is such an arrangement or the like that a capsule having put a resin is placed in a pressure vessel or container, is set, and compressed air is delivered into the pressure container by a compressor, thereby compressing the capsule to push the resin out thereof.
As described above, in the case where the crack width is large, it is possible to relatively easily pour the repairing agent such as the cement milk or mortar into the cracks and, thus, it is possible to easily repair the cracks. Generally, however, the cracks occurring in the concrete include many small ones equal to or less than 1 mm. On occasion, there are minute cracks of the order of a few micrometers. Accordingly, it is not necessarily easy to completely repair the minute cracks.
That is, in that case, the various appliances described above are used to inject the resin into the cracks. In order to practice complete injection, however, injection pressure larger than the injection resistance must be maintained for a long period of time. Further, since the injection resistance increases in proportion to the length of the cracks and the depth thereof, it is required that the injection pressure increases gradually. This is apparent from the Bernoulli theorem.
For the conventional method in which the above-described appliances are employed to inject the resin into the cracks, it is impossible to maintain of the injection pressure for long period of time and to increase the injection pressure gradually afterwards. Accordingly, it is impossible for any of the above-described appliances to sufficiently inject the resin into the cracks.
That is, in view of the mechanism for generating the injection pressure, all of the above-described appliances are characterized in that the injection pressure is maximum at the initiation point of injection, subsequently, is gradually reduced and, at last, approaches 0 (zero). Thus, it is impossible to retain the injection pressure necessary for the injection. For example, in the appliance illustrated in FIG. 12, the pressure within the rubber tube is maximum before the start-up of injection. When the injection starts and the quantity of the resin 2 within the rubber tube 1 decreases, the injection pressure is attenuated rapidly. This is the behavior which is against the injection theory in which the injection pressure must gradually increase. For the use of such appliance, it is impossible to practice complete injection. For the appliances illustrated in FIGS. 13 through 15, the circumstances are identical with the above ones.
The behavior of the conventional various appliances will be described in further detail with reference to FIG. 16. The abscissa in FIG. 16 indicates "a lapse of time from the start-up of injection or an injection length", while the ordinate indicates "the injection pressure of the appliance" and "the requisite injection pressure". The reference numeral 20 denotes a linear variation of the injection pressure in the conventional appliance, and the reference numeral 21 denotes a line indicating a varying condition of requisite injection pressure which is required for practicing complete injection.
In the figure, in the conventional appliance, the injection pressure is maximum at the point of time of injection start-up and, subsequently, is gradually attenuated. It is indicated, however, that the requisite injection pressure must gradually increase, conversely. It will be seen that, in spite of the fact that the injection pressure indicated by a point b is required at a point b', the use of the conventional appliance enables only injection pressure of almost 0 (zero) to be produced at the point b'. Further, the total energy required for practicing complete injection is indicated by an area enclosed by O-b-b', while the total energy generated by the conventional appliance is indicated by an area enclosed encircled by c-b'-O. In the case where the maximum injection pressure c of the appliance is equal to the requisite maximum injection pressure b, the total energy required for complete injection and the total energy generated by the appliance become equal to each other. Since, however, the injection requirements and the appliance capabilities are incompatible, half of the energy generated by the appliance is wastefully consumed. The energy used as the effective injection energy is only the area enclosed by O-a-b'. Since the energy encircled by O-c-a is generated at a stage which is not required for injection, not only the energy enclosed by O-c-a is not totally utilized effectively, but also bad effects are caused, such that the crack width is widened or, the concrete at the loosened crack portion falls off, and so on.
In the case where the conventional appliance is used, the complete injection cannot be practiced even if an appliance is used which can generate pressure equivalent to the injection pressure required for practicing the complete injection. That is, even if an appliance of 4 Kg of the conventional system when the maximum injection pressure is required by 4 Kg, repair cannot be practiced with respect to cracks in which the maximum requisite injection pressure is 4 Kg. In order to practice complete injection by the conventional appliance, the latter must be arranged such that the requisite injection pressure is produced at the final point in time. In the appliance, however, not only the maximum injection pressure becomes excessive at the time of injection start-up so that the bad influence like those described above occurs, but also the appliance must be large-sized in order to generate such large injection pressure. Large-sizing of the appliance causes handling problems, and causes large danger to be attended with. Thus, the appliance is not practical.
Furthermore, in the case where the above-described conventional appliances are used, it is possible to raise the injection pressure by addition of hydraulic pressure or by addition of a quantity of air. To this end, however, intervention of man power will be required and the injection operation becomes troublesome. This is also not practical.
In connection with the above, in FIG. 16, the varying condition of the requisite injection pressure is indicated in a straight line manner. In practice, however, the varying condition of the requisite injection pressure does not necessarily become linear attendant upon a change in the frictional resistance between the crack width and the periphery, and the varying condition of the injection pressure generated by the appliance does not become linear depending upon the structure or construction of the appliance. In either case, however, such a condition cannot be fulfilled that the maximum injection pressure is required immediately after injection start-up. Further, it is out of the bounds of possibility that, in the conventional appliance, the injection pressure becomes maximum at the final point in time.
Disadvantages of the repairing method, which utilizes the conventional appliances, will be summarized below:
1. The generation behavior of the injection pressure is opposite to the required condition of variation in pressure required for injection, and this is illogical.
2. In order to retain the injection pressure constant to practice complete injection, intervention due to man power is always required so that it is impossible to eliminate or reduce labor.
3. In order to produce high injection pressure, a complicated and large appliance is required, and special skilled laborers are always required.
4. Since the injection pressure cannot be maintained for a long period of time, it cannot be confirmed that injection becomes incomplete due to shortage or insufficiency of the injection pressure. In connection with the above, the above is applicable not only to the case where cracks generated in the concrete are repaired, but also equally to the case where repair is made to cracks in a base rock, and to cracks occurring in stone or brick, or in a masonry joint of a concrete block building.